Method of making molds



March 3, 1964 G. w. MERREFIELD 3,122,801

METHOD OF MAKING MOLDS Filed July 15, 1960 W 2/ 20 r 24 24 Ill/ll 1 25/ INVENTOR F GLENN w. MERREF/ELD BY M K/M ATTORNEYS United States Patent or ice grasses Patented Mar, 3, 1954 3,122,361 METHQEE GE MAKWG MQLDS Glenn W. hlerrefield, 212 Prospect St, Spring Lake, Mich. Filed July 15, 196i), Ser. No. 43,167 13 Claims. (Cl. 22-113) This invention relates to a method of making molds. viore particularly, this invention relates to a new and improved method of making metal castings utilizing a backup plate comprised of fused silica which remains with the mold through the casting of the article.

The foundry industry constantly searches for new and better methods to produce ferrous and non-ferrous castings. For many years, the foundry industry has used the shell molding process, forming a thin shell-like mold to the configuration of the article to be cast from a molding sand mixture and a resin binder and pouring the metal into such a mold. The shell molding process has some inherent disadvantages. First of all, the cost of the sandresin mixtures used to make the mold is usually quite high because of the need to produce strong rigid shells. The sand-resin mixture must contain from four to six percent resin order to provide a shell of sufficient strength and rigidity. When making the molds themselves, production is somewhat limited because of the dwell time required to cure the resin in the sand used. To some cases, where close casting tolerances are necessary, expensive m thods for backing up the shell molds have been devised. The resulting shell is thin and lacks the necessary strength to support the metal cast therein without external support. To provide this support, the shells are placed in containers, and surrounded by materials such as iron shot, sand, clamping fixtures and the like. These are generally known as backups. However, this still has not been entirely satisfactory.

In some instances, backups have been provided of cast run, one surface of the backup being shaped to the configuration of the outer surface of the article to be cast. In such a method, after the cast iron backups are formed, pa terns are placed within the backup and a molding sand mixture placed therebetween. Both the pattern and the cast iron backup must be heated when the sand is placed between them. Production is slow due to the dwell. time required to set the resin in the sand used for shell molding. The molding operation is delayed until the resin is set. Thus, this dwell time is the determ ing factor in timing the operation of the molding process. Furthe if either the pattern temperature or the temperature of the heated cast iron ba kup is not held to at least minimum curing temperature for the resin, a poor mold will be formed. Still further, when an article is cast in a mold utilizing a cast iron backup, the backup tends to distort as it expands with the application of heat. With repeated usage the distortion increases and becomes permanent. Consequently, after a limited period of usage, close tolerance castings cannot be obtained because of this distortion.

object of this invention is to provide backups comprised of fused silica, having a mold cavity therein shaped to the configuration of the mold to be used for the cast article.

Another object of this invention is to provide a method of making molds and a reinforced mold which enable castings to be produced to close dimensional tolerances. Further, these castings Will have an excellent surface finish.

Another object of this invention is to provide such a method which eliminates the use of certain complex and expensive equipment, together with elimination of substantial labor in the molding process.

Another object of this invention is to provide such a method which lowers the cost of the sand mixture used to form the mold, the mixture using urea base resins in place of phenolic base resins and lower percentages of resin binder than is used in conventional shell molding.

Another object of this invention is to provide a method which allows the blowing of the mold and the thermal setting of the resins to be performed in separate operations.

Another object of this invention is to provide such a method which does not utilize heated patterns, enabling the patterns to be comprised of lower cost materials such as wood, plastic, aluminum and the like.

Another object of this invention is to provide a method of molding, utilizing a backup plate, which allows the curing of the resin sand in the mold to be performed in a dielectric oven.

A still further object of this invention is to provide a method of molding utilizing backups, there being a minimum of distortion from repeated heating and cooling of the backup.

These and other objects of this invention will become obvious to those skilled in the art of molding, upon reading the following specification in conjunction with the accompanying drawings, wherein:

FIG. 1 schematically shows the steps of the method comprising this invention;

FIG. 2 shows a cross section of one embodiment of a shell mold making machine which may be used to practice the method of this invention, the molding machine being shown in draw position;

FIG. 3 is a view similar to PIG. 2, the shell mold making machine being shown in blow position; and

FIG. 4 is a cross sectional view of a mold for forming a cast article according to this invention.

Briefly, this invention relates to a method of metal castings consisting of the steps of providing a backup plate comprised of fused silica and having a recess therein shaped to the outer configuration of the mold to be used in the casting. A pattern plate having a pattern shaped to the configuration of the casting desired is positioned adjacent this backup plate. The area b ween the pattern plate and the backup plate is filled with a sand resin mixture. Heat is applied to the backup plate and sand mold therein, the heat being sufficient to set the sand mixture into a mold. The metal is then poured into this mold with the backup plate positioned therebehind.

Referring more specifically to the drawings, the reference numeral 26 (FIGS. 2 and 3) designates a backup plate of the type used to practice the method of this invention. The backup plate 2% is formed of fused silica and includes a recess or cavity 2?. shaped to the configuration of the mold to be used in the casting. A fused silica backup plate is not affected or distorted by normal molding temperatures. Further, such a plate may be eated in a dielectric oven. This material is strong, rigid and able to stand the required handling during molding processes with little or no breakage. it can also be made with varying degrees of permeability, to allow venting of gas from the mold and core materials. It should be noted that both cope and drag backups are provided, in order to form a completed mold as will be explained hereinafter.

FIGS. 2 and 3 show an exemplary shell mold making machine to be used in my process, structures of this general nature being old and well-known to the molding art. The backup plate Ztl is placed on a blower table 24 which is movably mounted on the blower base 23. A pattern 25 is mounted on the blow plate 26 below the blow chamber 27, lying above the backup plate 29. The backup plate 20 is adapted to be moved directly against the pattern 25 having a cavity or molding chamber 21 for the sand-resin mixture. The sand-resin mixture is blown in by compressed air from the blow chamber 27 through the tubes 28. It will be noted that no equipment is provided for heating either the backup plate or the pattern at the station where the sand-resin mixture is introduced. It is an aspect of this invention in that the step of heating may be and preferably is performed by other equipment at another station.

Turning to the schematic diagram shown in FIG. 1, the steps of providing the fused silica backup plate 20 together with a sand-resin mixture therein is designated by the reference numeral 1. It should be noted that lower cost urea base resins and a lesser percentage of resin binder may be used in the sand-resin mixture in this step of my method, thus making the mixture less expensive. This will be more fully explained hereinafter. Upon removing the pattern 25 from the backup plate, the backup plate 20 together with the sand-resin mixture compacted to the configuration of the pattern 2 5' in the cavity 21 is placed in a dielectric oven designated by the reference numeral 2. Since the backup 20 is comprised of fused silica, such an oven is extremely eificient. After the backup plate and sand-resin mixture have been heated, the backup plate is moved to station 3, where the backup plates and the shell mold are cooled. Next, at station 4, a cope and drag are properly positioned adjacent one another and clamped together. This mold is shown in FIG. 4, and includes a fused silica cope 26, a fused silica drag Zlla, a shell mold 29 and a cavity 30. Thus, the shell mold formed from the sand-resin mixture is completely enveloped by a pair of fused silica backup plates. This mold, together with the backup plates, is moved to the pouring station 5 where the metal is poured into the mold. This apparatus is then cooled at station number 6. At station number 7, the cope and drag are separated and the shell mold together with the cast article is removed from the backup plates. At station 8, the backup plates are cleaned for reuse and returned to station 9 where they will be used to cast another article. It will benoted that the sand-resin mixture may be provided from station it adjacent station 1.

Because the articles are cast with the fused silica backups in position behind the cope and drag of the mold, the sand mold can neither break. or distort. Consequently, the castings produced have close dimensional tolerances and smooth surface finishes. With these backups in place, lower cost sand-resin mixtures as described hereinbefore may be used because the backups produce the additional rigidity required for top grade casting. It is unnecessary to heat either the pattern or the backup at the time the sand is blown between them. Consequently, expensive machinery and equipment is eliminated at this stage of the molding operation. Further, since it is unnecessary to heat the patterns, they may be made of lower cost materials such as wood, plastic, aluminum and the like.

Because the sand is not heated at the time it is blown between the backup plate and the pattern, the production of molds is made much more efficient. With heated patterns, the equipment is tied up during the dwell time required to set the resin in the sand mixture. In my method, the backup is removed from adjacent the pattern as soon as the sand has been blown into the cavity provided 'thereii cnabIing another backup to be placed in position to make another shell mold. Since the backup is comprised of fused silica, a dielectric oven may be used to heat the sand mixture for curing the resin. Dielectric heating is more rapid than the conventional types of heating employed with cast iron backups. This in itself significantly decreases the length of the production time necessary to produce a shell mold. Such backups are not affected by the temperatures to which they are subjected in curing the sand-resin mixture and backing up the mold when the metal is poured therein. Consequently, distortion is virtually eliminated even though the backups are used repeatedly.

' It should be noted that it may be possible to practice the method of this invention through the use of certain changes or modifications without departing from the spirit and scope thereof. All such changes are considered to be a part of this invention as defined in the following claims.

I claim:

1. A method of making metal castings with a shell mold process consisting of the steps of providing a backup plate comprised of fused integral solid silica having a recess therein shaped to the outer configuration of the mold to be used in the casting; placing a pattern plate having a pattern shaped to the configuration of the casting adjacent said backup plate; filling the area between said pattern plate and said backup plate with a powderous sand-resin mixture; applying heat to said silica backup plate and said sand-resin mixture sufficient to set and cure said sand-resin mixture into a shell mold uniformly supported by said silica backup plate; and pouring metal into said mold with said backup plate positioned therebehind for support of all surface portions of the shell mold while casting said metal and burning out said resin; and then, after said metal cools, cleaning said burned-out resin and sand from said fused silica backup for repeated use of said backup.

2. A method of making metal castings with a shell mold process consisting of the steps of providing a backup plate comprised of fused integral solid silica having a recess therein shaped to the outer configuration of the mold to be used in the casting; placing a pattern plate having a pattern shaped to the configuration of the casting adjacent said backup plate; blowing a powderous sand-resin mixture into the area between said pattern plate and said backup plate with compressed gas; applying heat to said silica backup plate and said sand-resin mixture sufficient to set and cure said sand-resin mixture into a shell mold uniformly supported by said silica backup plate; and pouring metal into said mold with said backup plate positioned therebehind for support of all surface portions of the shell mold while burning out said resin; and then, after said metal cools, cleaning said burn-out resin and sand from said fused silica backup for reuse of said backup.

3. A method of making metal castings with a shell mold process consisting of the steps of providing a backup plate comprised of fused integral solid silica having a recess therein shaped to the outer configuration of the,

mold to be used in the casting; placing a pattern plate having a pattern shaped to the configuration of the casting adjacent said backup plate; filling the area between said pattern plate and said silica backup plate with a powderous sand-resin mixture; removing said silica backup plate and said sand-resin mixture from adjacent said pattern plate; applying heat to said silica backup plate and said sand-resin mixture sufiicient to set and cure said sand-resin mixture into a shell mold uniformly supported .ing out said resin; and then cleaning said burned-out resin and sand from said fused silica backup plate for reuse of said backup plate.

4. A method of making metal castings with a shell- 23 mold process consisting of the steps of providing a backup plate comprised of fused integral solid silica having a recess therein shaped to the outer configuration of the mold to be used in the casting; placing a pattern plate having a pattern shaped to the configuration of the casting adjacent said backup plate; filling the area between said pattern plate and said backup plate with a sand-resin mixture; removing said backup plate and said sand-resin mixture from adjacent said pattern plate; placing said backup plate and said sand-resin mixture into a curing oven for the application of heat to said backup plate and said sand-resin mixture sufiicient to set and cure said sand-resin mixture into a mold; and pouring metal into said mold with said backup plate positioned therebehind for support of surface portions of the shell mold while burning out said resin; and then cleaning said burned-out resin and sand from said fused silica backup for reuse.

5. A method of making metal castings with a shell mold process consisting of the steps of providing a backup plate comprised of fused integral solid silica having a recess therein shaped to the outer configuration of the mold to be used in the casting; placing a pattern plate having a pattern shaped to the configuration of the casting adjacent said backup plate; filling the area between said pattern plate and said backup plate with a sandresin mixture; removing said backup plate and said sandresin mixture from adjacent said pattern plate; placing said backup plate and said sand-resin mixture into a dielectric curing oven for the application of heat to said backup plate and said sand-resin mixture sufficient to set said sand-resin mixture into a mold; and pouring metal into said mold with said backup plate positioned therebehind for support of surface portions of the shell mold while burning out said resin; and then cleaning said burned-out resin and sand from said fused silica backup for reuse.

6. A method of making metal castings with a shell mold process consisting of the steps of providing a backup plate comprised of fused integral solid silica having a recess therein shaped to the outer configuration of the mold to be used in the casting; placing a pattern plate having a pattern shaped to the configuration of the casting adjacent said backup plate; blowing a sand-resin mixture into the area between said pattern plate and said backup plate with compressed gas; removing said backup plate and said sand-resin mixture from adjacent said pattern plate; placing said backup plate and said sand-resin mixture into a curing oven for the application of heat to said backup plate and said sand-resin mixture sufficient to set said sand-resin mixture into a mold; and pouring metal into said mold with said backup plate positioned therebehind for support of surface portions of the shell mold while burning out said resin; and then cleaning said burned-out resin and sand from said fused silica backup for reuse.

7. A method of making metal castings with a shell mold process consisting of the steps of providing a backup plate comprised of fused integral silica having a recess therein shaped to the outer configuration of the mold to be used in the casting; placing a pattern plate having a pattern shaped to the configuration of the casting adjacent said backup plate; blowing a sand-resin mixture into the area between said pattern plate and said backup plate with compressed gas; removing said backup plate and said sand-resin mixture from adjacent said pattern plate; dielectrically heating both said backup plate and said sandresin mixture in a dielectric curing oven for the application of heat to said backup plate and said sand-resin mixture suflicient to set and cure said sand-resin mixture and form a shell mold uniformly supported by said silica backup plate; and then pouring molten metal into said shell mold with only said backup plate positioned therebehind for support of surface portions of the shell mold; and then cleaning out said burned-out resin and sand from said fused silica backup plate for reuse of said backup plate.

8. A method of making a reinforced shell mold cope or drag of a molding apparatus for production of precision metal castings consisting of the steps of providing a backup plate comprised of fused silica and having a recess therein shaped to the outer configuration of the mold to be used in the casting; placing a pattern plate having a pattern shaped to the configuration of the casting adjacent said backup plate; filling the area between said pattern plate and said backup plate with a sand-resin mixture; applying heat to said backup plate and said sandresin mixture suflicient to set and cure said resin in said sand-resin mixture into a shell mold to form a combined sand-resin shell mold with a reinforcing, reusable silica backup plate.

9. A method of making a reinforced shell mold cope or drag for a molding apparatus for production of metal castings consisting of the steps of providing a backup plate comprised of fused silica and having a recess therein shaped to the outer configuration of the mold to be used in the casting; placing a pattern plate having a pattern shaped to the configuration of the casting adjacent said backup plate; blowing a sand-resin mixture into the area between said pattern plate and said backup plate with compressed gas; and applying heat to said backup plate and said sand-resin mixture sufiicient to set and cure said sand-resin into a shell mold having uniform reinforcing over all areas thereof by the silica backup plate.

10. A method of making a reinforced shell mold cope or drag for a molding apparatus for production of metal castings consisting of the steps of providing a backup plate comprised of fused silica and having a recess therein shaped to the outer configuration of the mold to be used in the casting; placing a pattern plate having a pattern shaped to the configuration of the casting adjacent said backup plate; blowing a sand-resin mixture into the area between said pattern plate and said backup plate With compressed gas; removing said backup plate and said sand-resin mixture from adjacent said pattern plate; applying heat to said backup plate and said sand-resin mixture sufficient to set and cure said sand-resin mixture into a shell mold having uniform reinforcing over all areas thereof by the reusable silica backup plate.

11. A method of making a reinforced shell mold cope or drag for a molding apparatus for production of metal castings consisting of the steps of providing a backup plate comprised of fused silica and having a recess therein shaped to the outer configuration of the mold to be used in the casting; placing a pattern plate having a pattern shaped to the configuration of the casting adjacent said backup plate; blowing a sand-resin mixture into the area between said pattern plate and said backup plate with compressed gas; removing said backup plate and said sand-resin mixture from adjacent said pattern plate; placing said backup plate and said sand-resin mixture into a curing oven for the application of heat to said backup plate and said sand-resin mixture sufiicient to set and cure said sand-resin mixture into a shell mold having uniform reinforciru over all areas thereof by the reusable silica backup plate.

12. A method of making a reinforced shell mold cope or drag for a molding apparatus for production of metal castings consisting of the steps of providing a backup plate comprised of fused silica and having a recess therein shaped to the outer configuration of the mold to be used in the casting; placing a pattern plate having a pattern shaped to the configuration of the casting adjacent said backup plate; blowing a sand-resin mixture into the area between said pattern plate and said backup plate with compressed gas; removing said backup plate and said sand-resin mixture from adjacent said pattern plate; placing said backup plate and said sand-resin mixture into a dielectric curing oven for the application of heat of said backups Within said recesses; and gate means for pouring metal into the mold cavity enveloped by said shell mold within said backup plates.

References Cited in the file of this patent UNITED STATES PATENTS Reene Jan. 16, Byrnes July 27, Devol Feb. 26, Hackett June 5, Wiedmann Aug. 2, Skoning Nov. 28, Jennings et a1. Feb. 12,

FOREIGN PATENTS Great Britain May 15, Great Britain Dec. 18, 

13. A MOLD FOR USE IN MAKING METAL CASTINGS BY A SHELL MOLD PROCESS, COMPRISING: A PAIR OF FUSED SILICA BACKUP PLATED, EACH OF SAID BACKUP HAVING A RECESS THEREIN SHAPED TO THE GENERAL CONFIGURATION OF THE ARTICLE TO BE CAST, SAID RECESSES POSITIONED IN FACE RELATIONSHIP; A THIN CURED SAND AND RESIN SHELL MOLD FORMED ON SAID BACKUP WITHIN SAID RECESSES; AND GATE MEANS FOR POURING METAL INTO THE MOLD CAVITY ENVELOPED BY SAID SHELL MOLD WITHIN SAID BACKUP PLATES. 